High frequency transmitter



Jail 3 D. H. VANCE HIGH FREQUENCY TRANSMITTER Filed Feb. 14, 1951 l5 Elli w mfim Mlll

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Inventor:

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Patented Jan. 5, 1932 u T-En smms' PA NToFFIce V DONALD E. VANCE, or s'cnENEo'rADY, NEW YORK; ASSIGNOR r GENERAL ELECTRIC, j

COMPANY, A CORPORATION OF NEW YORK HIGH FREQUENCY TRANSMITTER Application filed February 14, 1931. Serial No. 515,803. I a

My invention relates to high frequency transmitters and more particularly to means for keying or impulsing said transmitters in accordance withdesired signals. v In high frequency transmitters employing a number of cascade connected amplifiers difficulty is experienced in impulsing, or keying, the ,transmitted oscillations at high speed. This is due to the fact that ordinarily each of the cascade connected amplifiers of the system includes a tuned output circuit having a certain persistence of oscillation. Thus, if the disch argedevice of any amplifier earlyin the series isv rendered inoperative, as in keying, oscillations will persist in the ou put circuit of this amplifier for an interval thereafter having a durationdependentupon the characteristics .of the output circuit; During this interval these oscillations are supplied to the grid of the next amplifier of thecascade connection which is in'condition for amplification. This amplifier likewisehas a certain persistence, ofoscillationsand supplies oscillations tothe succeeding-amplr fier for an additional period, and so on through the entire series. Thus, when only the early stages of the series of amplifiersare controlled for keying purposes and the series includes one or more subsequent, amplifiers which are maintained in continuous condition for amplification, the total time interval required to interrupt the oscillations in the output circuitwof the transmitter is so great as to considerably reduce the keying speed at which satisfactory operation may be had.

On the other hand, if only one, or more, of

the .later'stages of the system is keyed difiiculty is encountered in interrupting the high currents involved with the rapidity necessary a to high speedsignaling. I

One of the objects ofmy invention, therefore is to provide means whereby the output froma high frequency transmitter may be keyed at high speed, as for example, for high as speed telegraphic, or facsimile, transmission,

and which at thesame time avoids the necessity for keying, or rendering inoperative in accordance with the signals to be transmitted,

1 more than a small portion of the amplifiers mits the master'oscillator of the system to be maintained in continuous operation and unaffected by operation of the keying means. The novel features which I believe to be Characteristic of my invention are set forth with particularity in the appended claims.

My intention itself, however, both as to its organization and method of operation, [together with further objects and advantages thereof, may best be understood by reference to the following descriptiontaken connec-, tion with the accompanying drawing in which the single figure represents an embodi; ment ofmy invention.

Referring to the drawing, Ihave represented therein a high frequency transmitter comprising a plurality of stages includinga master-oscillator 1 and a plurality ofcascade' connected" electron. discharge amplifiers 2 to 8 inclusive, whereby high frequency oscillations producedby the oscillation generator 1 are successively amplified and supplied to a suitable load circuit such as a radiating system which I have conventionally indicated at 9. Since the various amplifiers of thesystem may be assumed tobe of well known and conventional construction the circuit arrangement of only twoof these am plifiersis shown, these amplifiers comprising the-second amplifier from each end of theseries In the drawing I have shown these amplifiers 8 and 7, as being separated in the series by three amplifiers 4:, 5 and 6, but it will of course be understood that any greater or lesser niunberfof. amplifiers may be employed intermediate the two amplifiers 3 I and 7. The operation of amplifiers 3 and? is controlled by means. of a keying circuit which I have represented in the lower portion of the drawing thereby to interrupt the operation of each of the amplifiers 3 and 7 in ac cordance with the signals to be transmitted. It will be observed thateach of the amplifiers 3 and 7 has a tuned output circuit 10 in which oscillations persist after the discharge device of the amplifier has been rendered inoperative. During the interval in which these oscillations persist in the circuit 10 of amplifier 3 they are of course amplified by amplifiers 4, 5 and 6, which are continuously in condition for operation and the output circuits of which, similarly, have a certain persistence of oscillation after the supply of oscillations in the respective amplifier is interrupted. Accordingly, the interval over which the oscillations persist in the output of the last amplifier after the discharge evice of amplifier 3 has been rendered in operative is increased in accordance with the number of amplifiers which are maintained in condition for operation. If. however, one of the latter stages of the amplifier series is ke ed synchronously with the earlier am lifier ve satisfactory operation of the sysem may lie had at extremely high keying speeds.

The keying circuit of the transmitter comprises a plurality of electron discharge deteeters 11, 12, 13, 14, and a plurality of direct current amplifiers 16 and 17. Alternating current which is interrupted at the keying speed is supplied to the grids of the electron discharge detectors 111213 and 14,

by means of a transformer 15. The primary winding of this transformer, for example, may be connected to the output of a fac-simile machine, or other source of alternating current impulses, in accordance with which the transmitter is to be keyed. The opposite sides of the secondary winding of the transformer 15 are connected to the grids of discharge devices 11 and 13 through inductances 18 and 19 respectively, and similarly the opposite sides of this secondary winding are connected to the grids of discharge devices 12 and 14 through condensers 20 and 21, respectivel The oscillations supplied to the grid of ischarge device 13 is of course dislaced in phase by 180 from oscilations supplied to the grid of device 11, and similarly oscillations supplied to the id of discharge device 14 are displaced in phase by 180 from the oscillations supplied to the grid of discharge device 12. Because of the inductances 18 and 19 and the condensers 20 and 21, a 90 phase displacement is produced between the oscillations supplied to the grids of discharge devices 11 and 12, and 13 and 14. The anode circuit of the discharge devices 11, 12, and 13, 14, are connected in parallel and are energized, through a resistance 22, by a source of unidirectional electromotive force 23. The purpose of the phase adjusting arrangement used 111 the grid circuits of the devices 11, 12, 13 and 14, is to produce a relatively smooth unidirectional electromotive force across resistance 22, which is dependent in magnitude upon the alternating current supplied through the transformer 15 without the use of smoothing means in the output circuit of these discharge devices. This arrangement is more fully described and claimed in a copending application of Paul C. Gardiner, filed October 14, 1930, Serial No. 488,616, entitled Transmitting system, and which is assigned to the same assignee as m present application. The grid and catho e of dis c arge devices 16 and 17 are connected in parallel across resistance 22 so that the impedance between the anode and cathode of these discharge devices is controlled in response to the potential on resistance 22. The anode circuit of discharge device 16 includes a resistance 24 and source of potential 25 which are also included in the anode circuit of the amplifier 3. The anode circuit of amplifier 17 includes a source of unidirectional electromotive force 26 and a resistance 27, the latter resistance being also included in a circuit which extends from the grid of the discharge device of the amplifier 7 through a choke coil 28 and resistance 27 to the cathode of amplifier 7.

The operation of the arrangement may now be understood. Normall the potential supplied to the grid of the ischarge devices 16 and 17 is such that these devices are of comparatively low impedance and accordingly, a relatively high current flows in both of the anode circuits. This current flowing in the anode circuit of discharge device 16 causes a suflicient drop in voltage in resistance 24 to reduce the elect-romotive force appearing between the cathode and anode of amplifier 3 sufiieiently to render that device inoperative. At the same time the high current flowing in resistance 27 causes a sufficient negative potential to be applied to the grid of amplifier 7 to render the discharge device of that amplifier inoperative. Accordingly, notwithstanding that the oscillation generator 1 and the amplifiers 2, 4, 5, 6 and 8 are maintained in condition for operation, no oscillations are transmitted through the system or radiated from the antenna system 9.

When alternating current is present in the transformer 15, an increase in current is caused at each of the amplifiers 11, 12, 13 and 14. This current flowing in resistance 22 causes sufficient negative potential to be supplied to the grids of discharge devices 16 and 17 to cause those devices to become of high impedance. The high impedance of discharge device 16 reduces the current in resistance 24, and accordingly the drop in potential upon this resistance, thereby causing the anode potential of amplifier 3 to be increased sufliciently to permit eflicient operation of that amplifier. At the same time the increased impedance of discharge device 17 reduces the negative potential produced upon resistance 27, thereby causing the control grid of amplifier 7 to have a bias potential just suflicient for eflicient operation of that amplifier. Since all of the amplifiers are now in condition for efficient operation, the oscillay sired the first and second stages, comprising the oscillation generator 1 itself, may be keyed and similarly, the last stage comprising amplifier 8. Better operation, however,

may be had if the oscillation generator is maintained continuously in operation and the keying effected entirely by control of the amplifiers. Further, in order that the frequency produced by the oscillation generator 1 be unaffected by the keying operation, it is preferable that there should be at least one stage of amplification between the oscillation generator and thefirst stage of amplification which is controlled. The circuits of the output of the amplifier used in the last stage are of course coupled with the I antenna 9, which comprises a circuit having high resistance. Accordingly, the persistence of oscillation in the output circuit of this amplifier is not great. Because of the high power rating of this stage and its low persist ence of oscillation, I have found that it preferable that this stage be maintained in continuouscondition for operation and that the preceding stage be-controlled in accordance with the keying impulses.

While I have shown a particular embodiment of my invention it will of course be,

understood thatI do not wish to be limited thereto since many modifications both in the circuit arrangement and in the instrumentalities employed may be made without departing from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is 1. A high frequency transmitter, comprising a plurality of stages including an oscillation generating stage, and a plurality of amplifying stages, said amplifying stages being arranged for successive amplification of oscillations generated by said generating stage, and means to impulse said transmitter in accordance with desired signals, said impulsing means comprising means for rendering at least two of said stages which are separated by one or more intermediate stages, inoperative in accordance with said signals, said intermediate stage or stages being maintained continuously in condition for operation.

2. In a transmitter, the combination of a being separated in the cascade connection by at least one of said discharge devices, said one discharge device being maintained continuously in condition for operation.

3. The. combination of a high frequency transmitter comprising a source of oscillations and a plurality of amplifying stages arranged in cascade, the first stage being arranged to receive oscillations from said source andeach of said stagesincluding a resonant circuit having a certain persistence of oscillation whereby each stage operates to supply oscillations to the succeeding stage after the supply of oscillations to the respective stage is interrupted, and means to impulse the output from said transmitter at high speed, said means comprising means for interrupting the operation of two of said stages widely separated in said cascade arrangement whilethe stages intermediate said two stages are maintained in condition for operation.

4. Ina high frequency transmittenan oscillation generator, a load circuit, a chain of cascade connected amplifiers arranged between said load and said source, and means to interrupt the operation of at least two of said amplifiers in accordance with desired signals, said two amplifiers being separated in said chain by at least one additional amplifier which is maintained in continuous condition for operation and the first of said two amplifiers being separated from said oscillation generator by a second amplifier which is maintained in continuous condition for operation.

5. In a high frequency transmitter, an oscillation generator, a load circuit, a chain of cascade connected amplifiers arranged between said load and said source and means to interrupt the operation of at least two of said amplifiers in accordance with desired signals, said two amplifiers being separated in said chain by at least one additionalamplifier which is maintained in continuous condition for operation and the last of said two amplifiers being separated from said load circuit by an amplifier of larger power than the other of saidamplifiers, said larger power amplifier also having an output circuit having low persistence of oscillation.

In wltness whereof, I have hereunto set my hand.

DONALD H. VANCE.

plurality of cascade connected electron discharge devices, one of said devices being arranged to generate oscillations and to supply said oscillations to a succeeding discharge 1 device in said cascade connection and each of the other of said discharge devices being arranged to operate as amplifiers, and means to interrupt the operation of at least two of said discharge devices, said two discharge devices 

